Receiver having tunable amplifier with integrated tracking filter

ABSTRACT

A receiver is disclosed. The receiver includes: a tunable low noise amplifier (LNA), the tunable LNA comprising: a plurality of LNAs for receiving and amplifying a plurality of frequency bands respectively; a plurality of first switches respectively coupled to the plurality of LNAs; a plurality of LC loads, respectively coupled to the plurality of first switches; a plurality of buffers, respectively coupled to the plurality of first switches; and a plurality of second switches, respectively coupled to the plurality of LC loads and an LO signal; a power detecting circuit for determining a signal power level corresponding to the LO signal; a first switch unit; and a controller, for isolating the output of the plurality of LNAs, selectively decoupling at least one of the LC loads according to the signal power level of the LO signal, and routing the LO signal to the second switches during calibration mode.

CROSS REFERENCE TO RELATED APPLICATIONS

This application cites U.S. Pat. No. 6,940,365 and U.S. Pat. No.7,127,217, which are included herein by reference.

BACKGROUND

The present invention relates to the tuning of integrated LC filters,and more particularly to the tuning of integrated LC filters inbroadband television receivers.

Modern receiver systems utilize broadband technology to receive a widerange of frequencies. In order to prevent in-band blockers frominterfering with the receiver operation, a receiver requires very highlinearity at its front end. In broadband television receivers, aconventional method of achieving high linearity in the presence ofin-band blockers is to utilize Automatic Gain Control (AGC). A desiredsignal together with the in-band blocker are applied to a conventionalreceiver and amplified utilizing a broadband Low Noise Amplifier (LNA)and a Variable Gain Amplifier (VGA). A Wide Band Power Detector, coupledto the output of the VGA, converts the desired signal and blocker powerto a DC voltage, which is then input to the base-band part of thereceiver. As the DC voltage is directly proportional to the input signalpower, the base-band is able to detect the presence of strong blocker(s)if the corresponding base-band Radio Signal Strength Indicator (RSSI)level is not proportional to the WBPD DC level. When this occurs, thebase-band will send a signal to the front end to decrease the gain ofthe VGA. As the gain decreases, however, the receiver noise figure willalso increase. Therefore, the use of AGC is limited.

Many receivers therefore utilize tracking filters to amplify only thedesired input signal, thus reducing the need for such high linearity. Ina direct conversion receiver the tracking filter can track the internalLocal Oscillation (LO) signal generated by a phase locked loop (PLL).The frequency response of a filter refers to the characteristic(s) ofthe filter that conditions the input/internal signal to the filter. Thefilter will show frequency responses based on certain circuitparameters.

In a broadband receiver, a filter is required that has many frequencyresponses, i.e. a tunable filter. Prior art receivers utilize radiofrequency (RF) tracking filters, which are equivalent to band-passfilters. U.S. Pat. No. 6,285,865, which is included here for reference,discloses a receiver with such a tunable filter. The disclosedintegrated chip comprises: a first adjustable on-chip filter having afirst plurality of selectable capacitors that determine its centerfrequency; a second adjustable on-chip filter having a second pluralityof selectable capacitors that determine its center frequency; means forselecting a number of the first plurality of capacitors to adjust thefirst filter to a desired center frequency; and means for transferringthe selection of the first plurality of capacitors to the secondplurality of capacitors to adjust the second filter to a centerfrequency proportional to the desired frequency. The receiver describedneeds to calibrate a dummy tunable filter first before transferring theresults from the dummy filter to the other tunable filter in the mainsignal path. The need to duplicate and tune another tunable filter ispartly due to the fact the tuning of the filter in the main signal pathwill be affected by interferences coming from the antenna. This causesthe die area to increase unnecessarily.

Recently, other receivers incorporating integrated tracking filters havebeen developed. U.S. Pat. No. 7,127,217 is included as an illustration,and shown in FIG. 4. In this prior art, the entire receiving pathincluding the down-mixers must be configured to receive the filteredsignal from the tunable filter. In addition, the calibration signal willradiate through the antenna if an additional antenna switch is notpresent.

In both prior arts, the calibration of these tunable filters must eitherbe done in the factory to prevent radiation through the antenna, oroutside the signal path. A receiver comprising an integrated trackingfilter that minimizes interference to the receiver and prevents theradiation of calibration signal into the air during the filtercalibration process is needed. If the entire receiver path is notrequired during the tuning process, receiver power consumption may bereduced even further.

SUMMARY

It is therefore an objective of the present invention to introduce areceiver having an integrated tracking filter. A method thereof is alsointroduced.

The disclosed receiver comprises: a tunable low noise amplifier (LNA),for tracking to a local oscillation (LO) signal during a calibrationmode, the tunable LNA comprising: a plurality of LNAs for receiving andamplifying a plurality of frequency bands respectively; a plurality offirst switches respectively coupled to the plurality of LNAs; aplurality of LC loads, respectively coupled to the plurality of firstswitches; a plurality of buffers, respectively coupled to the pluralityof first switches; and a plurality of second switches, respectivelycoupled to the plurality of LC loads and the LO signal. The disclosedreceiver also comprises: a power detecting circuit, coupled to theoutput of the tunable LNA, for determining a filtered signal power levelcorresponding to the LO signal; a first switch unit, coupled to the LOsignal; and a controller, coupled to the power detecting circuit, thefirst switches, the second switches, and the first switch unit, forcontrolling the first switches to isolate the output of the plurality ofLNAs, controlling the second switches to select one of the LC loadsaccording to the frequency of the LO signal, and controlling the firstswitch unit to route the LO signal to the second switches during thecalibration mode.

The disclosed method comprises: providing a tunable Low Noise Amplifier(LNA) having a plurality of LNAs and a plurality of LC loads coupled tothe plurality of LNAs; selecting a desired LNA and a LC loadcorresponding to the desired LNA; isolating the desired LNA from theselected LC load; generating a local oscillation (LO) signal; routingthe LO signal to the selected LC load; determining a first filteredsignal power level of the LO signal with the WBPD; changing thecapacitance in the selected LC load; determining a second filteredsignal power level of the LO signal; comparing the first filtered signalpower level to the second filtered signal power level; and according tothe comparison result, determining whether to adjust the capacitance inthe selected LC load.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an exemplary embodiment of a receiver comprisingan integrated tracking filter.

FIG. 2 is a diagram of the integrated tracking filter

FIG. 3 is a flowchart detailing the tuning method of the receiver inFIG. 1.

FIG. 4 is a diagram of a conventional receiver.

DETAILED DESCRIPTION

Certain terms are used throughout the description and following claimsto refer to particular components. As one skilled in the art willappreciate, electronic equipment manufacturers may refer to a componentby different names. This document does not intend to distinguish betweencomponents that differ in name but not function. In the followingdescription and in the claims, the terms “include” and “comprise” areused in an open-ended fashion, and thus should be interpreted to mean“include, but not limited to . . . ”. Also, the term “couple” isintended to mean either an indirect or direct electrical connection.Accordingly, if one device is coupled to another device, that connectionmay be through a direct electrical connection, or through an indirectelectrical connection via other devices and connections.

The disclosed receiver utilizes an integrated filter for tracking to anLO signal, wherein the filter includes a plurality of LC banksintegrated in a Low Noise Amplifier (LNA). The filter works by tuningthe LC banks to the LO signal in a calibration mode.

Please refer to FIG. 1. FIG. 1 is a diagram of an exemplary embodimentof the disclosed receiver 200. In this embodiment the receiver is adigital direct conversion receiver, however, the disclosed invention andmethod are also applicable to other receivers. The receiver 200comprises an antenna 202 coupled to a tunable Low Noise Amplifier (LNA)204. The output of the tunable LNA 204 is coupled to a power detectingcircuit 206, comprising a Variable Gain Amplifier (VGA) 207 coupled to aWide Band Power Detector (WBPD) 209. The output of the VGA 207 is alsocoupled to a plurality of down mixers 221, 223, which down convertreceived signals to base-band signals. A phase locked loop (PLL) 212 inthe receiver 200 is coupled to buffer 217, which is in turn coupled tothe output of the tunable LNA 204. A first switch unit 214 is coupled tothe input of the tunable LNA 204. A controller 220 is coupled to thefirst switch unit 214, the tunable LNA 204, and the power detectingcircuit 206.

The tunable LNA 204 in FIG. 1 is made tunable by integrating a pluralityof LC loads into the amplifier. Please refer to FIG. 2. FIG. 2 is adiagram of the tunable LNA 204. The tunable LNA 204 includes a pluralityof band LNAs 232, 234, 236 coupled to a plurality of first switches 242,244, 246 respectively. The plurality of first switches 242, 244, 246 isfurther coupled to LC loads 252, 254, 256 comprising the integratedfilter. Each LC load 252, 254, 256 is coupled to a buffer 262, 264, 266respectively, and coupled to the LO signal by means of a plurality ofsecond switches 272, 274, 276.

During calibration mode, an LNA (e.g. 232) is selected from theplurality of LNAs 232, 234, 236 and a corresponding LC load (e.g. 252)is selected from the plurality of LC loads 252, 254, 256 according tothe frequency of the desired signal.

Next, an LO signal is generated according to the frequency of thedesired signal and routed to the tunable LNA 204 by the buffer 217. Thefirst switch unit 214 is for shorting the tunable LNA 204 input duringtuning. The controller 220 controls the first switch unit 214 to open orclose and the buffer 217 to turn on or off. The LNAs 232, 234, 236,down-mixers 221, 223 and the base-band circuits coupled to the output ofthese down-mixers are turned off during this mode. In addition, thebuffer (e.g. 262) corresponding to the selected LNA is turned-on. Theother buffers 264, 266 will be turned off.

All the first switches 242, 244, 246 are opened during calibration. Thisfurther has the function of isolating the LC load from the antenna 202.The operation of the plurality of second switches is controlled by thecontroller 220. The LO signal will then be passed to one of the selectedLC loads 252, 254, 256 and the filtered LO signal power level measuredwith the WBPD. Then capacitance of the LC load is changed, and thefiltered LO signal power level measured again. If the second filteredsignal power level is higher than the first filtered signal power level,the capacitance in the LC load has been changed correctly and the filteris being tuned in the correct direction. This process will continueuntil the filter is centered.

During normal operation, the selected LNA (e.g. 232), the correspondingfirst switch (e.g. 242) is closed to couple the selected LNA to thetuned LC load (e.g. 252), the corresponding buffer (e.g. 262) is turnedon and the first switch unit 214 is open, enabling input signals to bepassed to the tunable LNA 204.

In one embodiment, during the calibration mode, all capacitances in theselected LC load are switched in. The filtered LO signal is passedthrough the VGA 207 and the signal power then determined by the WBPD209. A unit capacitance is then removed from the LC load, and the signalpower of the filtered LO signal determined again. If the first signalpower level is lower than the second signal power level then thecalibrating procedure must be repeated once more, by removing more unitcapacitances from the selected LC load. Once the filter is centered thenthe tuning phase can be exited.

Please refer to FIG. 3. FIG. 3 is a flowchart detailing an exemplaryembodiment of the calibration mode of the disclosed receiver. The stepsare as follows:

Step 400: Open the first switch unit 214;

Step 402: Select an appropriate LNA from the plurality of LNAs 232, 234,236 (e.g. 232) along with a corresponding first switch from theplurality of first switches 242, 244, 246 (e.g. 242), a LC load from theplurality of LC loads 252, 254, 256 (e.g. 252), a buffer from theplurality of buffers 262, 264,266 (e.g. 262) and a second switch fromthe plurality of second switches 272, 274, 276 (e.g. 272) according todesired input signal frequency;

Step 404: Power off all un-selected LNAs (234, 236), buffers (264, 266)and down-mixers 221, 223;

Step 406: PLL 212 lock to generate LO signal according to desired inputsignal frequency;

Step 408: Open first switches 242, 244, 246 in LNA 204 and closeselected second switch (e.g. 272);

Step 410: Power on buffer 217 to route LO signal to LNA 204;

Step 412: Switch in all capacitance in selected LC load (e.g. 252);

Step 414: Detect signal power level (x) of filtered LO signal at VGA 207output utilizing WBPD 209;

Step 416: Remove one unit capacitance from LC load (e.g. 252);

Step 418: Detect signal power level (y) of filtered LO signal at VGA 207output utilizing WBPD 209;

Step 420: Is x>y? If yes go to Step 424, if no go to Step 422;

Step 422: Remove a next unit capacitance from LC load (e.g. 252), setx=y and go back to Step 418;

Step 424: Power off buffer 217;

Step 426: Open first switch unit 214 and selected second switch 272,close selected first switch (e.g. 242);

Step 428: Power on selected LNA (e.g. 232).

Please note that the above method is for a single pole LC, however, thedisclosed method and apparatus can also be applied to a tracking filterhaving more than two LC poles. In this case, steps 418˜422 will berepeated for each pole until all poles are centered, and the method willthen proceed to step 424. Both embodiments fall within the scope of thepresent invention.

By implementing the tracking filter after the tunable LNA 204, thetracking filter can be isolated from front-end interference and thecalibration signal (LO signal) will not radiate into the air via theantenna 202. Implementation of first switches 242, 244, 246 in thetracking filter, and the first switch unit 214 at the tunable LNA 204input further ensure these benefits. Furthermore, by integrating thetracking filter in the tunable LNA 204, the filter can be tuned directlyin the signal path.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

1. A receiver, comprising: a tunable low noise amplifier (LNA), fortracking to a local oscillation (LO) signal during a calibration mode,the tunable LNA comprising: a plurality of LNAs for receiving andamplifying a plurality of frequency bands respectively; a plurality offirst switches respectively coupled to the output of the plurality ofLNAs; a plurality of LC loads, respectively coupled to the plurality offirst switches; and a plurality of second switches, respectively coupledto the plurality of LC loads and the LO signal; and a power detectingcircuit, coupled to the output of the tunable LNA, for determining asignal power level corresponding to the LO signal; and a controller,coupled to the power detecting circuit, the first switches, the secondswitches, for controlling the first switches to isolate the output ofthe plurality of LNAs, and controlling the second switches toselectively couple one of the LC loads to the LO signal during thecalibration mode.
 2. The receiver of claim 1, wherein the powerdetecting circuit comprises: an amplifier, coupled to the output of thetunable LNA; and a power detector, coupled to the output of theamplifier.
 3. The receiver of claim 1, being a direct conversionreceiver.
 4. The receiver of claim 3, being a DVB direct conversionreceiver.
 5. The receiver of claim 1, further comprising: a first switchunit, coupled to the input of the tunable LNA, for shorting the input ofthe tunable LNA to a predetermined voltage level during the calibrationmode.
 6. The receiver of claim 5, wherein the first switch unit iscoupled to the controller, and the controller controls the first switchunit to short to the predetermined voltage level during the calibrationmode.
 7. The receiver of claim 1, wherein the capacitance of the LC loadis changed based on the value detected by the power detecting circuit.8. The receiver of claim 1, further comprising a plurality of buffers,respectively coupled to the plurality of LC loads.
 9. A method of tuninga receiver, the method comprising: providing a tunable Low NoiseAmplifier (LNA) having a plurality of LNAs and a plurality of LC loadscoupled to the plurality of LNAs; selecting a desired LNA and a LC loadcorresponding to the desired LNA; isolating the desired LNA from theselected LC load; generating a local oscillation (LO) signal; routingthe LO signal to the output of the tunable LNA to generate a filtered LOsignal; determining a first signal power level of the filtered LOsignal; changing the capacitance in the selected LC load and determininga second signal power level of the filtered LO signal; comparing thefirst filtered signal power level to the second filtered signal powerlevel; and according to the comparison result, determining whether ornot to adjust the capacitance in the selected LC load.
 10. The method ofclaim 9, wherein the step of determining a first filtered signal powerlevel of the LO signal comprises: amplifying the filtered LO signal; anddetermining a first signal power level of the amplified and filtered LOsignal; and the step of determining a second filtered signal power levelof the LO signal comprises: amplifying the filtered LO signal; anddetermining a second signal power level of the amplified and filtered LOsignal.
 11. The method of claim 9, wherein the step of isolating thedesired LNA from the plurality of LC loads further comprises: shortingthe input of the desired LNA.
 12. The method of claim 11, wherein thestep of shorting the input of the desired LNA comprises: providing acontrol signal; and opening a switch unit in response to the controlsignal.
 13. The method of claim 9, wherein the step of according to thecomparison result, determining whether or not to adjust the capacitancein the selected LC load comprises: if the first filtered signal powerlevel is greater than the second filtered signal power level, continuingto change the capacitance.
 14. The method of claim 9, wherein thereceiver is a direct conversion receiver.
 15. The method of claim 14,wherein the receiver is a digital direct conversion receiver.